The present invention relates to methods and apparatus for treatment of tree trunks to produce an elongated trunk of substantially rectangular crosssection. In the prior art methods of treatment of tree trunks, the effort has been made to use the most possible volume of wood of tree trunks in producing such articles as boards, girders, square timbers or the like where boards are normally removed from the main portion of the trunk so as to produce the trunk of the cross-section where wood of the trunk is utilized in the best possible fashion.
It is to be considered that each tree trunk does not have a uniform cylindrical shape. However, even in the ideal case, the trunks, in their natural condition, normally are slightly tapering towards their ends. Therefore, in almost every case, the trunks have bendings along the length thereof or even shape declinations. These declinations from the cylindrical shape lead to the fact that the lateral edges or boards do not extend straightly and uniformly along the length of the trunk, and particularly in the normal case, in the conically-shaped trunk, the boards extend forward each other as the cross-section of the conically-shaped trunk decreases toward the top of the trunk so that one can observe slopes or rough slabs on the surface of the trunk.
It is therefore desirable to produce cutting of boards from the main portion of the trunk, which will become a final product in the trunk treatment, at the relatively small sections of the elongated trunk. One of the known methods of cutting boards from the trunks is disclosed in the German published application DE-OS No. 2750712. In this method, rotary circular saw blades are utilized which make transversal cuts after the boards or lateral portions have been removed from the trunk. In the disclosed methods, the boards separated from the trunk still lay on the surface of the trunk so that the outer surface of the main portion of the trunk may be damaged by circular blades during producing the above mentioned transversal cuts. In order to avoid this disadvantage a splitting wedge is normally utilized which is placed into a gap between the boards and the main portion of the trunk. At the same time support for clamping previously cut boards on the trunk should be provided during the producing of transversal cuts.
The necessity of utilizing of a splitting wedge to be inserted between the boards and the trunk leads to considerably high manufacturing expenses. Furthermore, friction which occurs when the splitting wedge is placed into the aforementioned gap prevents the trunk from the required relatively fast advancing movement in the lengthwise direction, so that at one hand, the advancing speed of the trunk is limited by that friction and at the other hand, there is no sufficient available time to produce as many transversal cuts as desirable. More transversal cuts, are, however desirable when the portion of the trunk having slopes and rough slabs to be cut off is relatively long and some additional transversal cuts may be therefore required for subsequent separation of the slabs from the wood to be used to obtain the desirable shape of the trunk.
It has been therefore found desirable to provide such a method of cutting boards from tree trunks where the transversal cuts could be produced quickly and without additional guiding and/or clamping of the boards on the body of the trunk during making of the transversal cuts.
The trunks to be placed into the apparatus for cutting the boards are sometimes preliminary premachined so that they are formed with substantially rectangular cross section and have four substantially rectangular cutouts produced at each corner of the trunk. These cutouts are normally milled out from the trunk beofre boards are separated from the main portion of the trunk. Such method of premachining of trunks is disclosed, for example in the German patent application No. P 29 28949.4 which discloses sawing one of two angularly adjacent surfaces and removing residual material in in form of wood clips by milling, whereupon the next following saw cut is made along the other of the two surfaces.
With this method the boards obtained are limited at all sides thereof by saw cut, but they still have to be sorted and trimmed at their ends where portions of the bark area remain. The necessity for these additional operating steps is evidently undesirable.